The present invention is directed to an access control system for transmitting data from a central station to a plurality of receiving stations and method therefor and more specifically to a system where the transmitted data is real time stock market quotations.
The transmission of proprietary data to several receiving stations or users via either wire or radio entails security problems. That is, if the user is to be charged for the information, there must be some technique for preventing its free reception. Thus, in pay television the signal is scrambled and a decoder is provided which is attached to the user's television receiver. Billing information may be based on a flat rate per month basis or per program use where the use is monitored either by a two-way transmission over the cable or by periodic visits to the home.
Where the device to receive information, for example, stock quotations is a small portable hand-held radio receiver unit, the smallness and portability of the receiver make it difficult to adopt the same kind of system as is used, for example, for pay television. Thus, it is an object of the present invention to provide an improved access control system and method therefor for transmitting data from a central station to a plurality of receiving stations especially where the receiving stations are of the portable hand-held radio receiver type.
In accordance with the above objects, there is provided an access control system for transmitting data from a central station to a plurality of receiving stations. Each of the receiving stations comprises first memory means for permanently storing a unique serial number. A second temporary memory means stores an access code which includes in scrambled form the serial number, a service cutoff date, and also includes a cypher pointer. Map means are responsive to this cypher pointer for unscrambling the scrambled serial number and cutoff date. Finally, there are means for comparing the unscrambled serial number with the permanently stored serial number for validating each receiving station.
A corresponding method includes the steps of using a common map at both the central station and all of the receiving stations for scrambling the bits of an access code at the central station and unscrambling such bits at the receiving station. Each receiving station is provided with a unique serial number which is part of the access code. Permanently stored in each of the receiving stations is the serial number. This is compared with the serial number which is part of the access code after such code is unscrambled.